Higher alkyl esters of phosphonic acids



United States Patent HIGHER ALKYL ESTERS 0F PHO'SPHONIC ACIDS Forrest J.Watson and Rupert C. Morris, Berkeley, and John L. Van Winkle, SanLorenzo, Caliii, assignors to Shell Development Company, Emeryville,Calif., a corporation of Delaware No Drawing. Original applicationNovember 13, 1950, Serial No. 195,456. Divided and this application June30, 1953, Serial No. 365,252

8 Claims. or. 260-461) This invention relates to novel esters ofphosphonic acids with branched-chain alkyl alcohols containing at least8 carbon atoms in each of the alkyl groups, all of the alkyl groups insaid esters being identical in structure. The present application is acontinuation-in-part of copending application Serial No. 195,456, filedNovember 13, 1950, now abandoned.

The increasing complexity and greater precision of machinery employed inmodern industry creates an evergrowing demand for compounds andcompositions which will provide adequate lubrication for the movingparts of such machinery under all conditions of operating temperaturesand pressures. It has been found that natural lubricating oils, whetheremployed alone or in combination with various additives, are notentirely suitable for certain types of applications. Therefore, a largenumber of synthetic lubricants have been prepared and tested. Many ofthese are suitable only for specialized.

applications; others find wider applicability, according to their natureand characteristics. Increasing interest has been shown regarding theuse of various compounds containing phosphorus as lubricants for a Widevariety of applications. This interest has been based, for the mostpart, on the fact that many such phosphorus-containing compounds possessdesirable lubricating characteristics, such as the ability to lubricatetwo surfaces, each moving in relation to the other at high speeds underextreme conditions of pressure and temperature. These compounds havesome shortcomings as lubricants, however, for many of them cause anundesirable amount of corrosion of the alloys commonly employed asbearings in modern high-speed machinery. Particularly, it has been foundthat many phosphorus-containing compounds are highly corrosive withrespect to the so-called hardmetal bearing alloys, such as copper-lead,cadmiumnickel and cadmium-silver alloys. In many cases, the corrosivityof the lubricant increases with the length of its use-due todecomposition of the lubricant. Such lubricants may cause corrosion toalloy bearings of the copper-lead type to the extent of mg./cm. andeven,

greater when such bearings are submerged for hours or less in an airagitated oil which has been pre-oxidized at about 340 F. for 25 to 50hours.

It is our discovery that certain novel esters of phosphonic acids withthe same branched-chain alkyl alcohol containing at least 8 carbon atomsin the alkyl group possess highly desirable characteristics aslubricants and that such esters exhibit but a minimal amount ofcorrosivity toward the common hard-metal bearing alloys. Therefore, itis an object of the present invention to provide lubricants for modernindustrial machinery that give excellent lubrication of bearing surfacesover a wide range of speeds, pressures and temperatures without causingexcessive corrosion of the bearing alloys of that machinery. The novelcompounds of the invention also possess great resistance todecomposition under oper- "ice.

ating conditions and provide continuous, dependable lubrication over anindefinite period of time.

The ester compounds of the present invention may be represented by thefollowing general formula:

0 (R),.1 (oR),,.

where all the groups represented by R are identical in structure and arebranched-chain hydrocarbon groups, each of which contains 8 or morecarbon atoms. It is preferred that the hydrocarbon groups be alkylgroups containing from 8 to 15, inclusive, carbon atoms. The symbol m isa small integer selected from the group, 1 and 2, and the symbol It is asmall integer, m and n always having the relationship m+n=3.Representative compounds falling within this group are:bis(2-ethylhexyl) Z-ethylhexanephosphonate, di(isooctyl) isooctanephosphonate, 2-ethylhexyl bis(2-ethylhexane)phosphonate, isooctyldi(isooctane)phosphonate, bis(2,2,4-trimethylpentyl)2,2,4-trimethylpentanephosphonate, 2,2,4- trirnethylpentyl bis2,2,4-trimethylpentane) phosphonate, bis(3,5,5 trimethylhexyl) 3,5,5,trimethylhexanephosphonate, bis(2-methyl-3-ethylpentyl)2-ethyl-3-ethylpentanephosphonate, tetramethylbutyl bis(tetramethylbutane)phosphonate, Z-methylheptyl bis(2-methylheptane)- phosphonate,bis(2,4,5,7-tetramethyloctyl) 2,4,5,7-tetramethyloctanephosphonate,7,8-dimethyltetradecyl bis(7,8 dimethyltetradecane)phosphonate,bis(2,7-dimethyloctyl) 2,7-dimethyloctanephosphonate, 4-ethyll1eptylbis(4-ethylheptane)'phosphonate and bis(2,6-dirnethylheptyl) 2,6-dimethylheptanephosphonate. A particularly desirable group of thesecompounds consists of alkyl esters of primary phosphonic acids in whicheach of the alkyl groups contains 8 to 10 carbon atoms.

The generic term phosphonic acids employed herein and in the claimsincludes both primary phosphonic acids (general formula: RP(O)(OH)2) andsecondary phosphonic acids (general formula: R2P(O) (OH)), the Rsrepresenting substituent groups linked to the phosphorus atom by directcarbon-to-phosphorus bonds. The term phosphonate is used to designatethe esters of phosphonic acids. The term neutral ester is used todesignate esters of phosphorus acids in which all of the acid groups areesterified. This terminology is in accord with that stated inKosolapoff, Organo-Phosphorus Compounds, Wiley and Sons (1950), at page4 thereof.

The compounds of the present invention can be prepared by theisomerization of neutral alkyl esters of phosphorous and phosphonousacids, in which esters the alkyl groups are branched-chain and containat least 8 carbon atoms each, to form the corresponding esters ofprimary or secondary phosphonic acids. This isomerization can beeffected by the use of catalytic amounts of a lower alkyl halide. In thereaction, the phosphorus shifts from the trivalent to the pentavalentstate, the additional two valence bonds being occupied by an OX0 oxygenatom (=0).

The reaction may be illustrated generally by the following equations:

where R is defined as above, R is a lower alkyl group and X is a halogenatom.

This method of preparing the compounds of the inreactant involved. Inpreferred practice the reaction temperature is maintained within therange of from about 130 C. to about 190 C.

The reaction time should be suflicient to provide practical conversionto the desired product. The reaction time may be varied over the rangeof from about 1 to about 24 hours, as required, although in mostinstances a substantially shorter time, e. g., from about 1 to about 12hours is entirely adequate.

The process may be carried out in a batchwise or a continuous manner,and at substantially atmospheric pressure, although superatmosphericpressure of from about 2 atmospheres to about atmospheres may beemployed.

The novel compounds of the invention thus may be prepared convenientlyin accordance with this process by reacting together a neutral, or full,ester of a phosphorous acid or a phosphonous acid and a lower alkylhalide. As the phosphorus ester there may be employed a triester of aphosphorous acid-a trialkyl phosphite-with the same branched-chainaliphatic alcohol, the alcohol containing more than 8 carbon atoms, andpreferably from 8 to 10 carbon atoms. Suitable trialkyl phosphites whichmay be employed include, among others, tris(2-ethylhexyl) phosphite,tris(isooctyl) phosphite, tris(2,2,4-trimethylpentyl) phosphite,tris(tetramethylbutyl) phosphite, tris(Z-methylheptyl) phosphite,tris(2,4,5,7-tetramethyloctyl) phosphite, tris(7,8-dimethyltetradecyl)phosphite, tris(2,7-dimethyloctyl) phosphite and tris(4- ethylheptyl)phosphite. A particularly desirable group of these compounds comprisesthose compounds containing 8 to 9 carbon atoms.

Instead of a trialkyl phosphite, there may be suitably employed an alkyldiester of a phosphonous acid-a dialkyl alkanephosphonite-wherein thealkyl and alkane groups are the same, and each contains at least 8carbon atoms and preferably from 8 to 10 carbon atoms. Suitable dialkylalkanephosphonites include, among others, bis(3,5,5 trimethylhexyl)3,5,5 trimethylhexanephosphonite, bis(2-ethylhexyl)Z-methylhexanephosphonite, bis(7,8-dimethyltetradecyl)7,8-dimethyltetradecanephosphonite, bis(2-methyl-3-ethylpentyl)2-methyl-3-ethylpentanephosphonite, bis(isooctyl) isooctane phosphonite,bis(2,5-dimethyloctyl) 2,7 dimethyloctanephosphonite andbis(2,4,5,7-tetramethyloctyl) 2,4,5,7-tetramethyloctanephosphonite. Aparticularly desirable group of these compounds is that in which thecarbon chain contains 8 to 9 carbon atoms.

As the lower alkyl halide, there may be employed any monohalide of analkane having not over 3 carbon atoms in the chain. Examples of thiscatalyst include, among others, methyl iodide and bromide, ethyl iodideand propyl bromide. In the preferred practice of the process, the alkylhalide is the monohalide of methane, and the most suitable member ofthis limited group has been found to be methyl iodide.

The isomerization of the neutral ester of a phosphorous or a phosphonousacid can be effected by heating the mixture of reactant and catalysttogether at an elevated temperature. The lower alkyl halide is added tothe phosphorus ester in an amount just sufiicient to cause the halide toact as a catalyst and not as a reactant. In general, the amount of loweralkyl halide added to the reaction mixture will constitute not over 10%(on a molar basis) of the amount of the phosphorus ester present, andthe amount of the halide added preferably lies within the range of fromabout 2% to about 7% (on a molar basis) of the amount of the esterpresent in the reaction theatre.

The reaction temperature ordinarily lies within the range of from about100 C. to about 250 C., the optimum temperature depending largely uponthe particular The desired product may be obtained from the reactionmixture by (a) shaking the reaction mixture thoroughly with successiveportions of 1 N sodium hydroxide solution until a separate causticaqueous layer is obtained, followed by (b) thorough washing withsuccessive portions of warm water until the organic reaction mixture isneutral, and (c) distillation of the mixture to remove the lower boilingcomponents.

The following examples are presented for the purpose of illustrating thepreparation of the compounds of the invention. It is to be understoodthat the invention is not intended to be restricted to the specificcompounds stated and that other specific modifications are included bythe invention. In the examples parts are parts by weight, unlessotherwise indicated.

EXAMPLE I Bis(Z-ethylhexyl) Z-ethylhexanephosphonate was prepared byintroducing 480 parts of tris(Z-ethylhexyl) phosphite and 10 parts ofmethyl iodide into a reaction vessel, and heating the mixture for 3hours at 160 C. The amount of methyl iodide used represented 6% of theamount of the phosphite, calculated on a molar basis. Following theperiod of heating, the mixture was cooled, 300 ml. of 1 N sodiumhydroxide solution was added, and the whole mixture agitated thoroughly.Then another 200 ml. of the caustic was added and the mixture agitatedagain. The organic liquid phase was allowed to separate from the aqueousliquid phase, and the latter removed. The organic liquid was then washedthoroughly with successive 50 ml. portions of warm water until theorganic liquid was neutral. The organic liquid was then distilled, 286parts of product being obtained. This represented a conversion of 59.5%.The product had an acid number of zero, a density (20/4) of 0.9098, arefractive index (20/d) of 1.4472 and a boiling point at 5 mm., mercurypressure, of 210 C. The per cent phosphorus calculated to be present was7.41; the per cent phosphorus found to be present was 7.3. The prodnothad a viscosity at 100 F. of 8.71 centipoises, and at 200 F. a viscosityof 2.3 centipoises. The viscosity index is 79.

EXAMPLE II Di(isooctyl) isooctane phosphonate was prepared fromtri(isooctyl) phophite. 327 parts of tri(isooctyl) phosphite and 7 partsof methyl iodide were heated together in a reaction vessel at atemperature of -170 C. for 9 hours. The amount of halide was equal to0.65% (on a molar basis) of the phosphite. The mixture was then treatedfor separation of the product by the method stated in Example I. 205parts of product were obtained, representing a conversion of 62.6%. Theproduct had an acid number of 0.02, a density (20/4) of 0.9116, arefractive index (ZO/d) of 1.4471. The per cent phosphorus calculated tobe present was 7.41; the per cent phosphorus found to be present was7.6. The product had a viscosity at 100 F. of 11.26 centipoises and aviscosity at 200 F. of 2.76 centipoises. The viscosity index was 93.

EXAMPLE III ular interest for use as hydraulic fluids or as componentsof hydraulic fluids, and as lubricants for turbo-prop propulsionsystems. Because of their stability and their compatibility with a widerange of other compounds, the

Preparation of bis(3,5,5-trimethylhexyl) 3,5,5-tri- 1 d b d l f thmethylhexanephosphonate. Mix 460 parts of tris(3,5,5- 5 nave i g i euse9 p as.lclzers or Syn trimethylhexyD phosphite and 7 parts of methylbromide as We as Or.natura y occumng resms in a reaction vessel andheated at for The following data demonstrate the superiority of thehours. Cool the reaction mixture and separate the product compounfis ofInvention over compounds dlsclosefi by the method Stated in Example LThe product is by the prior art which are taught to be valuable assynthetic tained in substantial yield. 10 lutglcantsd I d H d d 1 d thompoun s an are compoun s we ose 1n e EXAMPLE Iv prior art; CompoundsIII and IV are exemplary of the 3,5 ,5 -trimethylhexylbis(3,5,5-trimethylhexane)phoscompounds of the invention.

Table I (B) Viscosity Index Small-Scale Oxidation-Corrosion (E) 0 a F 11901 1 1; (0) D W htL m ompoun or ua N90 oi n (DZ-ID) erg oss (mg /em$19M Cu Mg Fe ca Al Compound I-Dibuty1 n-octane-phosphonate (C4H9O)z(GaH7)PO 0. 02 (-65 85 155 24.2 2.32 0 6.16 0 46.2 Compound II-Dibuty1hexadecane-phosphonate (G4H90)1(C1UHN)PO 0.03 +45 149 149 20.7 0.08 0.280.24 0. 04 5.3 Compound IIIBis(2-ethy1hexy1) 2-ethy1- hexanephosphonate(OaHr10)2(CsH11)PO 0.00 -95 79 127 1.12 0.32 0.44 0.64 0.16 0.1 CompoundIV-Di (isooetyl) isooctanennnsnhnnate (CaH 7O)2(CsH17)PO 0.02 90 93 1260.84 0.16 0.00 0.12 0.00 0.31

phonate is prepared by following the procedure of Ex- We claim as ourinvention: ample III, with the single exception that 444 parts ofbis- 1. A phosphorus ester having the formula (3,5,5-trimethylhexyl)3,5,5-trimethylhexanephosphonite is substituted for the phosphitereactant.

EXAMPLE v 0=P(oR 368 parts of bis(7,8-d1methyltetradecyl)7,8-d1methyltetradecanephosphonite are isomerized to7,8-dimethyltetradeoyl bis(7,8-dirnethyltetradecane)phosphonate by whereall the groups designated by the symbol R" are heating with 6 parts ofmethyl iodide at 170 C. until the identical in structure, and arebranched-chain alkyl isomerization is complete. The product is separatedfrom p each group Containing at least 8 Carbon atoms. the the reactionmixture by the procedure stated in Example I. symbol represents aninteger selected from the group The compounds of the invention may alsobe illustrated of numbers conslstlllg 0f 1 and and the ym l 1 by thefollowing examples: represents an integer equal to 3 minus m.

a Bis(2-methy1-3-ethylpenty]) 2-methyL-3-ethy1pen- 2. Ab1s(d1alky1)alkane phosphonate 111 Which the alkyl lanephosphonate h hStructural formula; and alkanes groups are the same, and each consistsof a branched-chain alkyl group containing at least 8 carbon H atoms.(CBHWCHWHI) OHOHHEIO-CHTCE(ofiflcmoflmhll 3. A bis( dia1kane)alkylphosphonate in which the alkyl b. Z-ethylhexylbis(2-ethylhexane)phosphonate: and alkane groups are the same, and eachconsists of a branched-chain alkyl group containing at least 8 carbon c.Tetramethylbutyl bis(tetramethylbutane)phosphonate:

atoms.

4. Bis(3,5,5-trimethy1hexyl)3,5,5-trimethy1hexanephosphonate.

5. Bis(2-ethy1hexyl)Z-ethylhexanephosphonate.

d. Bis(2,4,5,7-tetramethylocty1) 2,4,5,7-tetramethyloctanephosphonate:

6. Bis(isooctyl)isooctane phosphor-late. 7. 2-ethy1hexylbis(2-ethylhexane)phosphonate.

e. Bis(4-ethylheptyl) 4-ethylheptanephosphonate:

Example VI The novel compounds of the invention, because of theirstability and rheologicial properties, are of partic- Kosolapoif: Iour.Amer. Chem. Soc., V. 67, pages 1180-2 (1945).

1. A PHOSPHORUS ESTER HAVING THE FORMULA